Bevel Not Working On Car Seat Model
This is likely to be an issue due to clamping, which prevents the bevel from generating non-manifold (i.e. self-intersecting) geometry. Try turning this off in the modifier settings and you should see what's happening. It'll probably be due to some of the very short edges meaning the clamping causes the bevel width to be clamped very small (small enough to make the bevel virtually invisible).